FIG. 11 illustrates a conventional type inverter system for the air conditioner mentioned above. Specifically, FIG. 11 shows a structure of an air-conditioning inverter system mounted to an electric vehicle.
In FIG. 11, an inverter 101 is supplied power through two routes, one is from a main battery 102 and another is from a sub battery 103, both the batteries power an electric vehicle. Main battery 102 outputs ca. 250V to power a is driving system that may consume relatively a large amount of power.
Main battery 102 powers an air-conditioning compressor 105 via switching elements 104, and may also powers a motor for driving the vehicle.
Sub battery 103 outputs ca. 12V to power a control system for inverter 101 in general. Sub battery 103 may also power other loads consuming relatively little power, such as headlights, a fan motor, and/or windshield wipers and the like.
Typically, main battery 102 and the sub battery 103 are insulated when mounted in an electric vehicle and a hybrid car, and a negative terminal of sub battery 103 is grounded to the car body.
Included in inverter 101, the following elements on side (a) and enclosed by a broken line are supplied power by sub battery 103 (e.g. 12V power supply):
current detector 108, gate drive circuit 109, inverter temperature detector 112, induced voltage detector 110, inverter control microcomputer 107, and power circuit 106.
Power supply circuit 106 produces, for example, 5V to power microcomputer 107 and other ICs integrated circuits by means of, for example, the 12V supplied from sub battery 103. Aside from inverter 101, sub battery 103 may also power charging circuit 111 and compressor temperature detector 113.
Each element lying on the boundary between side (a) and side (b), on the broken line in FIG. 11, such as, for example, charging circuit 111, may be supplied power from both power supply systems in order to function properly. In other words, high voltage power from main battery 102 and low voltage power from sub battery 103 may supply elements lying on the broken line between side (a) and side (b) in FIG. 11. The "power supply system" may be defined as "a power source environment including a first power supply and other power supplies connected to one of the positive or negative terminals of the first power supply."
An air-conditioning controller 114 is supported, for example, by 12V from sub battery 103. Air conditioning controller 114 determines a desirable rotating speed of compressor 105 based on information supplied from occupants of a car and various sensors including an in-car temperature detector, and sends an instruction value associated with a rotating speed to inverter 101. Microcomputer 107 included in inverter 101 receives the instruction value, and sends a control signal to gate drive circuit 109 causing compressor 105 to run at a desirable speed. Based on the control signal, gate drive circuit 109 controls an ONIOFF state of plural insulated-gate-type bipolar-transistors (hereinafter called IGBT) that comprise switching elements 104. A waveform of voltage supplied to compressor 105 is a three-phase pulse width modulation (hereinafter called PMW voltage.
An example of the conventional air-conditioning inverter system described above is disclosed in the Japanese Patent Application Unexamined Publication No. H08-48140.
FIG. 12 illustrates a structure of another conventional inverter system, i.e. an air-conditioning inverter system incorporated in a home-use air conditioner. In the case of the home-use air-conditioner, power may be supplied from commercial power supply 215, e.g. single phase 100V. This power supply may be only available as a first power supply. The ac voltage of commercial power supply 215 may be rectified with rectifier diode 216 into a dc voltage, which may be supplied to compressor 205 via switching elements 204.
Power supply 215 may be insulated and its voltage reduced by isolation transformer 217. The resultant secondary insulated dc voltage may be supplied to air-conditioning controller 214 and charging circuit 211. The secondary insulated dc voltage may also be supplied to inverter 201 thereby producing, for example, a 5V power supply for a control system by means of power circuit 206. Power circuit 206 is thus typically incorporated into inverter 201. Such a 5V power supply may power inverter control microcomputer 207, current detector 208, gate drive circuit 209, and induced voltage detector 210. Charging circuit 211, current detector 208, gate drive circuit 209, and induced voltage detector 210 may be supplied power from two routes. In other words, some system components may receive a high voltage from power supply 202, and a low voltage from power supply circuit 206 and/or secondary insulated dc power 217.
FIG. 13 is a schematic diagram of a printed wired assembly board (hereinafter called PWA) of the conventional inverter. There are two circuit families, a first circuit-family may be driven by a main battery, for example, 102 or 202, and a second circuit-family may be driven by sub battery 103 or isolation 25 transformer 217.
FIG. 14 is a schematic diagram illustrating a conventional air-conditioning inverter system, such as the system shown in FIG. 11, that is mounted in an electric vehicle.
These conventional air-conditioning inverter systems, however, have a few drawbacks as follows.
First, two power supply systems are connected to inverter 101 or 201, which increase wiring.
Second, as two power supply systems that should be insulated from each other are connected to inverter 101 or 201, each member of the circuit families, which is driven by at least one of the two power supplies, needs an insulating space. Further, some circuit blocks that are driven by the two power supplies may need creepage distances (margin) on the PWA in addition to the insulating spaces within each block. These circuit blocks include components 108, 109, 110 and 111, or 208, 209, 210, and 211. As a result, the inverter system becomes larger, and insulation demands may increase the cost.
The inverter temperature detector, incorporated in the inverter, and the compressor temperature detector, i.e. detectors 112, 113 in FIG. 11 and 212, 213 in FIG. 12, should be insulated from the detecting targets per se such as the motor built in the compressor and switching elements. This also requires space due to insulation demands and may increase the cost. Further, in order to retain the insulation, it maybe better to place these detectors away from the detecting targets, i.e. the motor and switching elements, whereby a detection error may increase.
Third, the two circuit-families are insulated from each other, however, stray capacitances, as shown in FIG. 13, may exist between the two circuit-families.
These stray capacitances permit noise produced by switching, which is a noise source in the AM band, to be led from the first power supply system (high voltage driving system) to the second power supply system (low voltage driving system). The noise may also be easily transmitted outside the inverter. In addition, clock noise due to the operation of the inverter controlling microcomputer, which is a noise source in the FM band, are led from the second power supply system to the first power supply system. This noise may also be easily transmitted outside the inverter. The power lines are thus subjected to these noises and may radiate radiation noise interfering with the radio receiver and its antenna.